BANGKOK (AP) — A fire extinguisher exploded and killed a student during a fire drill held outdoors in sweltering heat at a high school in Thailand’s capital Friday, police said. Five other students were injured.

The carbon dioxide canister was being displayed in bright sunshine near students during the demonstration in Bangkok when it exploded and sent metal scraps into the chest of the boy who died, city police chief Thiti Saengsawang said.

Temperatures in Bangkok reached as high as 36 C ( 97 F) on Friday.

At least three people could face charges of death by negligence, Thiti said, but he did not identify them. Police and rescuers said five students were injured.

Education Minister Treenuch Thienthong said it was the first time in six years that the school had held a fire drill, and that it was coordinated by Bangkok's fire department. She said the department hadn’t experienced such an accident before during the many drills it has conducted at schools.